1) Field of the Invention
The present invention relates both to a method of piloting a rotary wing aircraft having a tail rotor that is suitable for pivoting about a swivel axis, and also to such an aircraft.
More particularly, the invention relates to aircraft provided firstly with a rotary wing for providing at least part of the lift of the aircraft, and secondly with a tail rotor suitable for countering the yaw torque generated by the rotary wing on the airframe of the aircraft, said tail rotor being capable of pivoting about an axis in order to contribute to propelling the aircraft.
2) Description of Related Art
The performances of a helicopter are conventionally limited by the speed of rotation of the main rotor that constitutes the rotary wing. In particular, the speed of the blades of the main rotor relative to the surrounding air must remain locally slower than the speed of sound. Thus, at high speed, the lifetime of the components is significantly reduced because of the appearance of vibration and because of the stresses introduced by the mast torser as generated by the cyclic pitch.
Consequently, in order to obtain a rotary wing aircraft capable of traveling at high speed for ecological reasons, e.g. for energy saving purposes, it is possible to make use of an additional source of propulsion, in particular to give access to high forward speed.
Document FR 1 511 006 suggests using a tail-mounted pusher propeller associated with a conventional helicopter antitorque tail rotor. The pusher propeller thus serves to off-load the main rotor of at least some of its propulsive functions.
In order to optimize the performance of a helicopter, document FR 1 017 976 suggests using an aircraft provided with a rotary wing and a tail rotor suitable for pivoting about a swivel axis.
In a primary mode of operation, the tail rotor is in a first position in order to counter the torque generated by the rotary wing and in order to control the yaw movement of the aircraft.
In a secondary mode of operation, the tail rotor is swiveled into a second position so as to contribute to propelling the aircraft, with yaw control then being obtained by steering the tail rotor on either side of a neutral position.
Under such circumstances, the first position is referred to for convenience below as the “stationary”, first position insofar as the tail rotor is “frozen” in a predetermined position during the primary mode of operation, with the aircraft then operating like a conventional helicopter. Conversely, the second position is referred to for convenience below as the “steerable”, second position, insofar as the tail rotor then moves through a predetermined angular sector during the secondary mode of operation.
Such an aircraft is sometimes referred to as a “vector thrust helicopter”. Document GB 599 990 also describes an aircraft of that type.
Document U.S. Pat. No. 3,155,341 presents a convertiplane having a main rotor, a swivel-mounted tail rotor, and a wing, which convertiplane is suitable for going from a helicopter mode to an airplane mode. The convertiplane is not a vector thrust aircraft, since the pedals are disconnected from the tail rotor in forward flight.
Document FR 1 536 412 describes a control mechanism for pivoting a tail rotor of a convertiplane. That mechanism has a single outlet relating to controlling the pitch of the tail rotor blades and two inlets for yaw control in helicopter mode and for thrust control in airplane mode, the translation from one kind of control to the other taking place progressively. Thus, in the secondary mode of operation, yaw control becomes inoperative, whereas in the primary mode of operation, thrust control is inoperative.